#include <string.h>
char *
strrev (char *str) 
{
    char *p1, *p2;
    if (!str || !*str)
	return str;
    for (p1 = str, p2 = str + strlen (str) - 1; p2 > p1; ++p1, --p2)
	 {
	*p1 ^= *p2;
	*p2 ^= *p1;
	*p1 ^= *p2;
	}
    return str;
}